I decided to try playing an all war game, something I rarely do. Therefore I picked Boduica, and went out with three warriors to crush my first opponent.

The three warriors went into Saladin's lands and found only 1 warrior defending his capital. I attacked into the city, and it automatically razed it. The borders of the city had expanded and it had 20% cultural defense.

Why did it raze the city without my permission? Any ideas?

Did you by any chance click One City Challenge (OCC) option ?

Sometimes the city is just destroyed in battle. At least you can keep the gold pilaged. If you use one of your own settlers to make a city on the exact spot, you can use all of his improvements.

zarakand,

Bigfoot3814 is correct. If the city is size 1 there is a chance the city will be destroyed when you take it over with swords (or any other military unit.) If you wait for the city to grow to size 2, I'm fairly sure you can avoid this, as I have never seen a size 2 city be auto-razed when it has been taken over by swords in a normal game.

if it was still size 1, it usually gets razed.

I didn't click OCC, as I'm building a settler to go rebuild Mecca. It's strange, I never knew that the city could just get randomly destroyed.

It's the first time that it has happened to me. Are the percentages of something like that happening fairly low? It's quite cool, troops go crazy and destroy a little too much. Sounds quite plausible to me.

Pretty sure if a city NEVER was above size one it will be razed upon capture. If it was ever above size 1 then the city will survive. This applies to barb cities as well, and since barbs cannot whip its is unlikely a barb city at size 1 was ever above size 1.

Ah it had never grown past size 1, as this was a very early war. I rushed 3 warriors out and a conquering we went! Good to know.

Keep in mind the BTS AI likes to whip units as a last ditch attempt

Pretty sure if a city NEVER was above size one it will be razed upon capture. If it was ever above size 1 then the city will survive. This applies to barb cities as well, and since barbs cannot whip its is unlikely a barb city at size 1 was ever above size 1.

Absolutely Correct.

I believe a city will also avoid autoraze if it's cultural border has popped. I think it was mentioned on another thread somewhere here.

I think that was in Civ III only and removed from Civ IV due to the obious exploit.